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Cruising and must run tilt all the way down

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dougtorr56

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I have new Bennington tritoon Model 22SXSB with a Mercury 150 HP outboard motor. Running the boat on the lake the trim must stay all the way down for smooth motor operation. If the motor is trimmed up even an 1/8 of the way, sounds like the prop is cavitating air and RPM becomes erratic in turns.

Any reasons for this?
 
What hole is the motor mounted?
 
20 or 25 inch shaft ? What size prop ?
 
Any pictures of a) motor and hole mounts, b) motor cavitation plate relative to pontoons when on the trailer or sitting dockside, and c) cavitation plate in water when going WOT?

Based on initial description I’d have guessed it is mounted too high, but then you report it being mounted as low as it will go. Pictures of the above might help some members chim in with ideas.

You’d typically need to trim down when in aggressive turns and at high speeds, but when going straight one would typically trim up some for optimal performance.

Curious, do you also have to keep it trimmed all the way down when going straight to avoid cavitation, light turns, or simply when in aggressive turns?
 
Vikingstaff said:
Any pictures of a) motor and hole mounts, b) motor cavitation plate relative to pontoons when on the trailer or sitting dockside, and c) cavitation plate in water when going WOT?

Based on initial description I’d have guessed it is mounted too high, but then you report it being mounted as low as it will go. Pictures of the above might help some members chim in with ideas.

You’d typically need to trim down when in aggressive turns and at high speeds, but when going straight one would typically trim up some for optimal performance.

Curious, do you also have to keep it trimmed all the way down when going straight to avoid cavitation, light turns, or simply when in aggressive turns?
Click to expand...

If it’s straight line…. I’d be thinking the motor is a 20” shaft instead of 25”….

@dougtorr56, do you have the motor model number? I’d be curious what’s on the build sheet, and to see if it matches what’s installed…. (Model/serial number from the actual motor). With that info we can tell you if it’s the short or long shaft model at least
 
Based upon my experience with boats and trim, each has their own unique setting. As I’ve mentioned before, with my current setup (GCW 2574, 250 Verado) the operational trim setting is all within the zero range. As such, at least as far as my boat is concerned, a 1/8 trim would be way too high unless I were in shallow water.
 
Welcome to the forum Doug! I've got the same motor! Love it! While underway is the cavitation plate on the motor even, below or above the waterline???
 
jcr159 said:
If it’s straight line…. I’d be thinking the motor is a 20” shaft instead of 25”….

@dougtorr56, do you have the motor model number? I’d be curious what’s on the build sheet, and to see if it matches what’s installed…. (Model/serial number from the actual motor). With that info we can tell you if it’s the short or long shaft model at least
Click to expand...
I was wondering the same thing.
Do you have two or three tubes?
If three, express or full length center tube?
2 tubes or express require 20" (L series merc engine)
All others will require 25" (XL series in merc engine)
 
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